The Plasmodium falciparum very early gametocyte stage gene, Pfg27/25, has a polymorphic locus upstreasm of the coding sequences which is surrounded by conserved sequences. The structure of the polymorphic region specifies accurate or altered blood stage specific transcription of the gene. The polymorphic structures arise by an as yet uncharacterizes DNA rearrangement. The overall objectives of this proposal are to determine the detailed structure of this locus in laboratory isolates that display different blood satge specific transcription patterns for the Pfg17/25 gene, and the extent to which these polymorphisms occur in nature. The 5' terminus of the Pfg27/25 mRNAs will also be determined to see where the transcription start sites occur with respect to the boundaries of the polymorphic domain.